1. Field of the Invention
This invention relates to a high-purity silicone ladder polymer of high molecular weight having hydrogen atoms in side chains, a silicone ladder prepolymer, and processes for producing them. A silicone ladder polymer of the invention can be advantageously used as a material for making protective films, inter-level insulation films, etc in semiconductors and other electronic devices.
2. Description of the Prior Art
Because of its unique molecular structure, a silicone ladder polymer excels in heat resistance, electrical insulating properties and chemical resistance. It have been conventionally been used as a material for making protective films and inter-level insulation films in electronic parts or semiconductor devices, etc.
For example, a conventional process for producing such a conventional silicone ladder polymer is described in Japan Patent Laid-open (Kokai) No. 124943/85. In this process, triethoxysilane is hydrolyzed in an organic solution and polymerized under a reduced pressure. The terminal thereof is modified with dimethylchlorosilane. The resultant is then purified with an organic solvent to yield a silicone ladder polymer.
The conventional process for producing a silicone ladder polymer had a problem that a silicone ladder polymer obtained contained large amounts of impurities or by-products. This is because the purification after modifying a terminal is not sufficient and the reaction after hydrolysis is conducted under conditions where impurities or by-products are hardly removed, e.g., at a high temperature of 35.degree. C. Further, since the molecular weight of the silicone ladder polymer obtained is as low as 100000 or less, there is another problem that the formation of a thick film is difficult.